This invention relates to a retrofocus type wide angle photographic lens having an aperture ratio of 1:2.5, a view angle of 85.degree. and backfocal length which is 1.5 times of the overall focal length sufficient to be mountable on an SLR (single lens reflex) camera, in which various aberrations are well compensated for.
A specific lens construction according to the present invention will be described herein. In the prior art various lens constructions for wide angle lenses are known. A lens construction disclosed in U.S. Pat. No. 4,062,622 has some similarities to that of the present invention and relates to a lens construction having an aperture ratio of 1:4.0 and a viewing angle of 95.degree.. The present invention relates to a lens construction having an aperture ratio of 1:2.5 and a viewing angle of 85.degree.. That is, in the present invention, although the view angle is somewhat narrowed, the aperture ratio is remarkably advanced. In this case, since the view angle is made small, astigmatism and distortion is compensated for with ease and it is also available to obtain a sufficient backfocal length.
However, since the aperture ratio is increased, it is difficult to compensate for spherical aberration and coma aberration. Unless the lens power arrangement is widely varied, it is difficult to compensate for the various aberrations with good balance. However, the present invention provides a lens system in which these aberrations are compensated for with good balance. As indicated, the present invention is an improvement on the U.S. Pat. No. 4,062,622 that realizes a lens system on the basis of another conception of lens design.